Fluorolog-3 v. 2.2 (11 Jul 2002)
Applications
10-3
Detecting sub-picomolar concentrations of
fluorescein
Instrument sensitivity is often expressed in terms of the
limit of detection
of a standard
substance. The superior sensitivity of Fluorolog
®
-3 systems is demonstrated by their
ability to detect sub-picomolar concentrations of standard substances such as fluo-
rescein. Often, other instruments perform this task by extrapolating from much higher
concentrations. The Fluorolog
®
-3, however, not only detects femtomolar concentrations
of fluorescein, but directly measures the true emission spectrum of 50-femtomolar fluo-
rescein using an integration of only 1 second—a clear demonstration of superior per-
formance.
Reduced-volume samples
Because the samples required to produce spectral data may be expensive or obtained
only in limited quantities, the precise imaging quality and photon-counting sensitivity
of the Fluorolog
®
-3 spectrofluorometers are invaluable assets. The following diagram
compares the fluorescence emission of 20-n
M
resorufin acquired using the 20-µL and
4-mL cells. Notice that the signal level is maintained with either cell.
Comparison of the fluorescence emissions of 20-n
M
resorufin using a 20-µL cell
and a 4-mL cell.
20 n
M
resorufin in
20-µL flowcell
20 n
M
re-
sorufin in 4-
mL flowcell
600 650 700
Wavelength
(nm)
Intensity (× 10
6
counts s
–1
)
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